Barometric pressure is measured using a barometer. A barometer is a device that measures atmospheric pressure. The most common type of barometer is the mercury barometer, which consists of a glass tube filled with mercury. The tube is inverted and placed in a dish of mercury. The height of the mercury in the tube is proportional to the atmospheric pressure.

Why is barometric pressure measured?

Barometric pressure is measured for a variety of reasons, including:

* To predict the weather. Barometric pressure can be used to predict changes in the weather. When the barometric pressure drops, it often indicates that a storm is coming. When the barometric pressure rises, it often indicates that clear weather is on the way.

* To measure altitude. Barometric pressure can be used to measure altitude. The higher the altitude, the lower the barometric pressure. This is because the weight of the air decreases as the altitude increases.

* To calibrate altimeters. Altimeters are instruments that measure altitude. Altimeters are calibrated using barometric pressure.

* To study atmospheric circulation. Barometric pressure can be used to study atmospheric circulation. Atmospheric circulation is the movement of air around the globe. By studying barometric pressure, scientists can learn about the direction and speed of the wind, and how these factors affect the weather.